Interaction of Tropical Deep Convection with the Large-Scale Circulation in the MJO

Abstract

To better understand the interaction between tropical deep convection and the Madden–Julian oscillation (MJO), tropical cloud regimes are defined by cluster analysis of International Satellite Cloud Climatology Project (ISCCP) cloud-top pressure—optical thickness joint distributions from the D1 dataset covering 21.5 yr. An MJO index based solely on upper-level wind anomalies is used to study variations of the tropical cloud regimes. The MJO index shows that MJO events are present almost all the time; instead of the MJO event being associated with “on or off” deep convection, it is associated with weaker or stronger mesoscale organization of deep convection. Atmospheric winds and humidity from NCEP–NCAR reanalysis 1 are used to characterize the large-scale dynamics of the MJO; the results show that the large-scale motions initiate an MJO event by moistening the lower troposphere by horizontal advection. Increasingly strong convection transports moisture into the upper troposphere, suggesting a reinforcement of the convection itself. The change of convection organization shown by the cloud regimes indicates a strong interaction between the large-scale circulation and deep convection. The analysis is extended to the complete atmospheric diabatic heating by precipitation, radiation, and surface fluxes. The wave organizes stronger convective heating of the tropical atmosphere, which results in stronger winds, while there is only a passive response of the surface, directly linked to cloud radiative effects. Overall, the results suggest that an MJO event is an amplification of large-scale wave motions by stronger convective heating, which results from a dynamic reorganization of scattered deep convection into more intense mesoscale systems.

Convective Characteristics of the Madden–Julian Oscillation over the Central Indian Ocean Observed by Shipborne Radar during DYNAMO

“…8d). This radar-based finding well matches the satellitebased finding that deep narrow (or isolated) convection is more prevalent during preonset MJO periods, while wide (or organized) convection is more common during active periods (Morita et al 2006;Tromeur and Rossow 2010;Riley et al 2011). Though the deep convective population decreases more than 40% when the active phase evolves to phase 3 (Fig.…”

“…More recent studies have investigated the MJO cloud population, precipitation structure, dynamical structure, and the interaction of convection with the large-scale environment using radiosonde or satellite sounding data (Kiladis et al 2005;Tian et al 2006), model reanalysis (e.g., Kiladis et al 2005;Benedict and Randall 2007), satellite precipitation retrievals (Tian et al 2006;Morita et al 2006;Benedict and Randall 2007), and satellite cloud measurements (Tromeur and Rossow 2010;Lau and Wu 2010;Virts et al 2010;Riley et al 2011;Del Genio et al 2012;Barnes and Houze 2013). These results showed that cloud systems across the MJO cycle basically progress from shallow cumulus, to cumulus congestus, to deep convection, and finally stratiform.…”

The Interaction Between Deep Convection and Easterly Waves over Tropical North Africa: A Weather State Perspective

“…Despite plausible features in these results, T B measurements are known to suffer from cirrus contamination (low T B may not always correspond to deep convective clouds, rather the satellite could be seeing a cold, nonprecipitating high cirrus cloud). Tromeur and Rossow (2010) show that OLR does not distinguish between the different kinds of convection that are identified by the ISCCP WS in the tropics. Tromeur and Rossow (2010) show that OLR does not distinguish between the different kinds of convection that are identified by the ISCCP WS in the tropics.…”

On the Increasing Importance of Air-Sea Exchanges in a Thawing Arctic: A Review

“…These exchanges drive global weather systems on scales ranging from individual thunderstorms to global circulation patterns [1][2][3][4], including polar lows containing hurricane-force winds exceeding 25 m s −1 [5]. Representing a primary conduit for atmosphere-ocean communication, air-sea interactions serve as the linchpin connecting the Earth's ocean and atmosphere [6,7].…”